The RALES study indicates that addition of spironolactone (S) to standard treatment (diuretics, ACE inhibitors, glicosides) of patients with congestive heart failure (CHF) (NYHA III-IV, EF ~ 25%) results in statistically and clinically significant prolongation of survival. OBJECTIVE: Cost-effectiveness analysis of S versus placebo in conjunction with standard treatment, in the management of CHF. METHODS: RALES results were used to estimate the increase in survival and the reduction in the number of hospitalisation arising from the use of S in management of CHF. Life-years saved were estimated from RALES data using survival curves analysis. Direct medical costs were estimated on the basis of Polish sources. The perspective of the health care payers and time frame of 2 years was taken. Decision model was used. Sensitivity analysis (Monte Carlo) was performed. RESULTS: S increased mean survival (1.41 month patient/2 years) and was cost saving, reducing direct medical costs for CHF patient over 2 years, 348 zl ($ 84.9). One-way sensitivity analysis indicated, that therapy with spironolactone remained cost saving even when drug cost was increased 4 times and the risk of hospitalisation in S group was increased by 20%. When 3 variables (frequency, hospitalisation cost, live-years-saved) were changed simultaneously, in 73.8% simulations ICER value was negative, and 90% were in range: - 21097/8524 zl. CONCLUSION: Addition of S to standard management of CHF in Poland should improve survival and may provide a net reduction in treatment costs. Economic significance is highlighted by 100 000/year hospitalisation due to CHF in Poland.